Oxidation-resistant mineral oil

ABSTRACT

A stable mineral oil composition comprises a base mineral oil to which has been added a synergistically acting mixture of heavy cycle gas oil and coal oil obtained from the distillation of coal tars. Preferably, at least one of the components of the composition has been subjected to mild hydrogenation.

United States Patent Henri Gourlaouen Mont-Saint-Aignan;

Christian Jahan, Bois-Guillaume; Robert Muths, Mont-Saint-Aignan; JeanTaillardat, Mont-Saint-Aignan, all of [72] Inventors France 21 Appl. No.885,970 [22] Filed Dec. 17, I969 [45] Patented Dec. 7, 1971 [73]Assignee Esso Research and Engineering Company [32] Priority Dec. 30,1968 [3 3] France [3 l 1816 18 [54] OXIDATION-RESISTANT MINERAL OIL [9Claims, No Drawings [52] US. Cl 208/14, 208/264, 252/63 [SI] lnt.ClI-IOlbS/ZZ [50] Field ofSearch 208/14, 19; 252/63 [56] References CitedUNITED STATES PATENTS 3,3 l8,799 5/l967 Acker et al. 208/14 PrimaryExaminer- Herbert Levine AtlorneysPearlman and Stahl and Frank T.Johmann ABSTRACT: A stable mineral oil composition comprises a basemineral oil to which has been added a synergistically acting mixture ofheavy cycle gas oil and coal oil obtained from the distillation of coaltars. Preferably, at least one of the components of the composition hasbeen subjected to mild hydrogenation.

OXIDATION-RESISTANT MINERAL OIL The present invention relates to mineraloils which are resistant to oxidation, and to a process for making suchmineral oils, and in particular, although not exclusively. the inventionrelates to such mineral oils which contain a significant proportion ofaromatic compounds, which thereby gives them a high degree of utility aselectrical oils.

It is well known that insulating oils have to perform very long-termservice in electrical apparatus. 1t is therefore particularly importantthat these oils should withstand oxidation well. The oils prepared bythe usual refining processes withstand oxidation better the closertheircontent of aromatic compounds is to an optimum value, which isrelatively low. Nevertheless, the insulating oils which, in modernelectrical apparatus, are subjected to ever higher electrical fields,must not only possess exceptional stability, but also have the propertyof dissolving any gases which may be liberated and form dangerouspockets in high-tension apparatus. This latter requirement is at presentincompatible with the previous one, since the oils absorb the liberatedgases better the more aromatic they are.

It is already known that the resistance of oils to oxidation is improvedby adding to them, in the course of refining, a small quantity of apetroleum fraction known in the trade as heavy cycle gas oil. Heavycycle gas oil will hereinafter be designated H.C.G.O. and isa'distillation fraction of heavy products that are formed, at the sametime as light products, in cracking operations, such as catalyticcracking operations, for instance.

The oils to which the H.C.G.O. is added are usually mineral oilsprepared by refining petroleum distillates or deasphalted residuesaccording to processes comprising various treatments, the most usual ofwhich are treatment by a selective solvent such as phenol or furfural toremove at least some of the aromatic compounds, dewaxing, treatment bysulfuric acid or oleum, treatment by an activated earth and forhydrogenation. The refining process is selected according to the natureof the crude and in accordance with the uses to which the oil is to beput, as required.

The H.C.G.O. is very rich in aromatic and heteroaromatic compounds. Tothe mineral oils are added about 4 percent by weight of H.C.G.O. Thearomatic character of the oil is thus enhanced, but the benefits of thisincrease in aromaticity are limited, for beyond the proportion of 4percent, which corresponds to an optimum, the incorporation of anadditional quantity of H.C.G.O. does not favorably influence thestability of the resulting oil blend.

It is also known that the stability of mineral oils can be improved bythe addition, in the course of refining, of a small quantity of a coaloil, as for instance, an anthracene or a chrysene oil, which oils arecharacterized by a high content of aromatic and heteroaromaticcompounds. The optimum proportion is between 0.5 and 2 percent of theweight of the base oil. Exceeding this proportion exerts an unfavorableinfluence on the stability of the oil. MOreover, oils treated by morethan 1 percent coal oil have a very unpleasant odor.

It has now been discovered that the combination of heavy cycle gas oiland coal oil exerts a synergistic effect on the resistance of mineraloils to oxidation.

It has also been discovered that it is possible to add a largeproportion of heavy cycle gas oil to a mineral oil to increase itsaromatic character without impairing its stability, provided that asmall quantity of coal oil is also added to the mineral oil.

The present invention therefore makes it possible to prepare mineraloils having both excellent resistance to oxidation and an aromaticcharacter, two properties which, according to the previous proposals,were incompatible.

The process of the invention comprises adding to a mineral oil, forpreference during refining, between 2 and 50 percent, or moreparticularly, between 3.5 and 25 percent by weight of heavy cycle gasoil, and between 0.1 and 5 percent or more particularly, between 0.2 and1 percent coal oil as it is or modified by preliminary treatments.

The heavy cycle gas oil (H.C.G.O.) may have very variablecharacteristics according to the regulation of the cracking unit and theway in which it is separated by distilling from the other productsderived from cracking. These characteristics are in general within thefollowing limits:

Density at c. 0. mm 1.100

Viscosity at 98.9 C.

( 210 F.) from 2 to 8 cat.

Aniline Point from to 80 C. Distillation between 180 and 660 (at normalatmospheric pressure) The H.C.G.O. can be topped by distilling beforebeing added to the base mineral oil. It is moreover advisable to dewaxit before adding the base oil, if the final oil is required to have acloud point (ASTM D 97.47) less than 5 C. For instance, by dewaxing aH.C.G.O. by the presently practiced processes, there is obtained with ayield of 80-85 percent, a product whose pour point is 1 5 C.; the finaloil treated with the H.C.G.O. thus dewaxed has a cloud point of C.

To increase the proportion of aromatics and heteroaromatics it is alsopossible to subject the H.C.G.O. whether or not dewaxed, before addingit to.the mineral base oil, to a suitable treatment, such as extractionby a selective solvent (phenol for instance) so as to obtain a yield ofextract or to 95 percent, and better still from to percent.

It is an advantage to subject the H.C.G.O., whether or not dewaxed, orits solvent extract, before adding it to the oil, to mild acidtreatment, such as treatment by 5 to 20 percent, and preferably 8 to 12percent by weight of sulfuric acid of 98 percent strength; the acid tarsare decanted hot (80 to 100 C.) then the acid raffinate is neutralizedby an aqueous or alcoholic solution of a mineral base, washed with waterand dried on a natural earth (silicoaluminate).

The coal oil, anthracenic oil or chrysene oil, is obtained by distillingthe tars derived from heat treatment of the coal, Its characteristicsare generally within the following limits:

Density at 15 C. 1.000 to 1.200 Flash Point (open vessel) to 200 C,Refractive index at 60 C.- 1.630 to L670 Freezing Point 50 to +30 C.sulfur 0.3 to 09 Z Nitrogen 0.6 to 1'1 C/H (atomic ratio) 1.35 to 1.65

Particularly interesting results are obtained with those anthracene oilstermed pale at 5 C." or pale at 0 C.

The coal oil may also undergo various classical treatments forpurification before being added to the base mineral oil.

The H.C.G.O. and the coal oil, whether or not treated as mention above,may be added to the base oil to be improved, for preference before afinishing treatment with natural or activated earth, or better stillwith hydrogen. Alternatively, the H.C.G.O., the coal oil, as they are orhaving undergone one or more of the treatments mentioned above, and thebase oil to be improved are subjected separately, or mixed in pairs orall together, to a finishing treatment (with natural or activated earth.or better still hydrogen) before mixing them.

The treatment with hydrogen can take in the presence of a hydrotreatmentcatalyst under the following ranges of conditrons:

Temperature (C.) 200-300, more preferably 210-280 Pressure (bars) 30-80,more preferably 40-70 Space Velocity (Vols. feedstock/Vol.catalyst/hour) 0.3-2.0, more preferably 0.8-L2 Volumes H (reduced toN.T.P.)/Vol. feedstock 100-400,

more preferably -250 The hydrotreatment catalyst may be any catalystsuitable for mild hydrogenation-for example, oxides and/or sulfides ofcobalt, molybdenum, nickel or tin, among others, and the catalyst may bedisposed on a supporting material such as silica or alumina.

it is possible, according to the aromatic nature of the raffinate andthe quantities of H.C.G.O. and coal oil added, to

prepare oils which meet different operational requirements. inparticular, it is possible to obtain exceptionally stable oils having anaverage aromatic character, or highly aromatic oils possessingsufficient stability.

A number of mineral oils will now be described by way of il- 5lustration only, some of the mineral oils being nonlimitative exemplaryembodiments in accordance with the invention and the others, which arenot in accordance with the invention,

being described by way of comparison. 1

EXAMPLE 1 Preparation of stable oils with medium aromatic character A330-410" C. light distillate derived from Tijuana crude l 5 was refinedby solvent extraction with phenol so as to obtain a raffinate having aviscosity gravity constant (VGC) equal to 0.822, the yield ofraffinatebeing 55 percent by volume. The parameter VGC is well known in the art,and is defined, for example, on page 82 of ABC du Graissage," apublication of the institut Francais du Petrole.

There was added to the light raffinate thus obtained (raffinate l) invarious hereinafter-disclosed proportions, a H.C.G.O. having thecharacteristics hereinbefore referred to, and a coal oil (an anthracenicoil termed pale at 0 C."), the characteristics of these components beingas tabulated in table (Volume of hydrogen )/Volume of oil) =l 50(volumes referred to normal conditions of temperature and pressure).

The resistance to oxidation of the various oils thus prepared -wasinvestigated the so-called BBC" (Brown Boveri Company) test whichconsists of heating to l C., 1,000 cc. oil in a copper pot in thepresence of a cotton thread. After 72 hours and I68 hours, respectively,the NPA color (ASTM D 155) and the acid number (ASTM D 947) of the oilare determined, and also the quantity of deposits and the percentage ofloss of resistance of the cotton thread. After I68 hours the dielectriclosses are also measured and given as the tangent of the angle of lossof the tested oil.

To determine the proportion of aromatic carbon, the ndM method is used(refractive index-density-molecular mass) giving the proportionofaromatic carbon as a function of these three parameters. The Brandesmethod furnishes the same results by infrared investigation. Theabsorption of liberated gas is found by the Pirelli method. Thisconsists of measuring,

under well-defined conditions (16 kv.300 minutes-80 C.) the tendency ofthe oil to absorb or desorb a gas (either hydrogen or nitrogen) withwhich the oil has previously been saturated.

A satisfactory oil must be able to absorb gas. Under the conditionsstated above, figures in the region of 1.2 cc. hydrogen TABLE II 011composition A B 0 Base Oil, Raifinate I 100 Anthracene oil (wt. percent)Aromatic carbons (percent by ndM method).

Absorption oi gases of hydrogen 0.8 0.8..... 0.85

(Pirelli method) cm. BBC test- 72 hours:

Colour (NPA) 4- 2 2 Acligrglmber, mg. 0. 140 0.040... 0.070... 0.050 0075 Deposits percent 0.024 0.010... 0.007 0.015.... 0 0.007. 0 017 0.020Percent loss ofreslstsnce 0 0....... l 0 0 0.

of cotton thread. 168 hours: 7

Colour (NPA) 5- 4..... 3- Acid number, mg. 0. 250 0. 09.... 0.07

KOH/g. Deposits, percent 0.078 0. 0.020 0.040. Percent loss of strength20 22 20 of cotton thread. Tangent of angle ot'1oss 0.2680 0. 0180..0.0105 0. 0300... 0.0170 0. 0700.. 0.0175 0.0250. Remarks on overallcharacter- Very poor Good. Excellent compared Good. Excellent comparedPoor-.- Good, but strong Very strong lstics and performance. with B.with D. smell smell.

1. are satisfactory. Nevertheless, certain users require higher ab-TABLE 1 sorption figures. The results obtained are given in table II,

wherein the different oils bear the references A to H.

The oil C in accordance with the invention, with the simultaneousaddition of H.C.G.O. and anthracenic oil, is charac- Pmpeny Amhmcenc 0terized by exceptional stability. It is found that this oil is morestable than Otis B and G which contain respectively the op- Densily 0390m8 timum quantity of H.C.G.O. by itself and the anthracenic oil sulmwm 30.54 by itself. The oil G has the further drawback of being evilNitrogen m 0. 8 smelling. Flush lfuim'open Oil E, which is also inaccordance with the invention, has f j 'g $71? 2 96 2 both excellentstability and gas-absorbing properties. Oil D pour'puimlc 45 has thesame capacity for absorption but does not contain anthracenic oil and isless stable than Oil E.

EXAMPLE 2 Preparation of more highly aromatic oils with good stability Alight distillate derived from Tijuana crude was refined by were preparedwith this raffinate (raffinate ll the oils referred to by the letters Ito N, whose characteristics are given in table Ill.

TABLE III Oil composition I J Base 011, Rafilnate II 100 100 H.C.G.O.(wt. percent) Anthracene 011 (wt. percent) Aromatic carbon (percent, ndMmethod). 11 12. Gas absorption (Pirelli method), cm. of 1.4 1.45

hydrogen. BBC test- 72 hours:

Colour (NPA) 4- 3- 2- Acid number, mg. KOH/g. 0.180-. 0.06"... 0.035.Deposits, percent 0.030-. 0.015.... 0.005. Loss of strength of cottonthread 0 0 168 hours:

Colour (NPA) 5 4- 35-- Acid number, mg. KOH/g 0 350.- 0.09 06-Deposition, percent .1 0.035.. 0015 4 Loss 01 strength of cotton thread27 11 15. Tangent 01' angle of loss (90 0.)... 0.3560 0.0300. 0.0170.0.04 0.0300 0.0420. Remarks on overall characteristics and per- Verypoor... Good. Excellent compared with J. Good. Excellent compared Verystrong odour.

formance. with L. Note high aromaticity.

The oils K and M of the invention, with the addition of C. andpale at0C." H.C.G.O. and anthracene oil, display exceptional gas-absorb- 10. Amethod according to claim 1 m which the base oil is a mg properties andexcellent stabllities compared with the oils rafiinate derived from asolvent extraction process. J. d an clea y de ons ate the syne gisticinterac- 11. A method according to claim 1 in which the base oil,

tion of the H.G.C.O. and the anthracene oils, despite the fact H C.G.O.and coal oil are subjected to a refining process in that compara lePI'OPOl'ti n f r i compounds are 2 5 any combination, the refiningprocess comprising contact with present in many ase 21 natural earth orhydrotreatment.

The present invention has been described by y of 12. A stable mineraloil made by a process in accordance planation but in no wayrestrictively. Any useful modifications i h l i 1, may he made to itWithout departing from its Scope as defined 13. A stable mineral oilcomprising a base oil of low arothe PP claims- I matic content, from 2to 50 wt. percent of heavy cycle gas oil We Claim and 0.2 to 1.0 wt.percent of coal oil, the heavy cycle gas oil 1. A method of making anoxygen stable oil composition having the f n i properties; whichcomprises adding to a light straight run distillate oil from which thearomatics have been removed by solvent ex- Dusky 5C. M90 traction from 2to 50 wt. percent of heavy cycle gas oil Viscosity ut91i.9C. 2 to a cat.

(H.C.G.O.) and from about 0.2 to 1.0 wt. percent of coal oil, n i Point25) we the weight percentages being based on the weight of the base rungmm Hg) oil. I 2. A method according to claim 1 m which the H.G.C.O. hasand the coal 0 having the following properties: the followingproperties: 40 I Densit at 15 C. 1.00 to 1.20 3222;152:1 3, C. 22: Flashoint (open vessel) 120 to 200 C. 0 o Refractive Index at 60 C. 1.63 to1.67 a P 25 Pour Point 0c.) w Distillation range (Cl 180") 560 Sum" (Ma)OJ m 0.9 (reduced m 760 Hg) Nitrogcn(wt.'1) 0.0 m |.0

C/H atomic ratio 1.35 to 1.65 3. A method according to claim 1 in whichthe l-1.C.G.O. has been dewaxed. 14. A stable mineral oil according toclaim 13 in which at A method according claim 1 in which the least oneof the base oil, heavy cycle gas oil and coal oil has been enriched inaromatic compounds y the use of a solvent been hydrotreated, in anycombination with the other oils. extraction PI 15. A stable mineral oilaccording to claim 14 in which the 5. A methodaccording to claim 1 inwhich the H.C.G.O. has heavy cycle gas oil has been dewaxed. been toppedby distillati n 16. A stable mineral oil according to claim 15 in whichthe 6. A method according to claim 1 in which the H.C.G.O. has heavyCycle gas oil i a dewaxed Solvent extract f a topped been subjected toan acid treatment. heavy cycle gas i] f ti A method according to claim 1in which the 17. A stable mineral oil according to claim 16 in which theforms the to 25 Percem Yelafive to base base oil is a mineral oil ofrelatively low aromatic content and A method according to claim 1 inwhich thfi coal oil has the heavy cycle gas oil is a dewaxed solventextract of an acidthe following properties: treated, topped heavy cyclegas oil fraction.

18. A concentrate for stabilizing mineral oils to oxygen Density at 15C.1.00 to 1.20 which consists essentially of about 28 to 99.8 wt. percentFlash point (open vessel) 120 to 200C. heavy cycle gas oil (H.C.G.O.)and 72 to 0.2 wt. percent coal Refractive lrldcx at 60 C. 1.63 to 1:87on. 2: 1;? 0 1:02 19. A method as claimed in claim 1 wherein saidcomposi- Nitrogen (wt.%) 0.6 to 1.0 tion is more stable than one madesolely from said distillate oil /H atomic ratio 1.35 m 1.05 and 2 to 50wt. percent of said heavy cycle gas oil or one made solely from saiddistillate oil and 0.2 to 1.0 wt. percent of said 9. A method accordingto claim 8 in which the coal oil has coal oil, been selected from theanthracene oils known as pale at 5

2. A method according to claim 1 in which the H.C.G.O. has the followingproperties: Density at 15* C. 0.990 to 1.100 Viscosity at 98.9* C. 2 to8 cst. Aniline point 25* to 80* C. Distillation range (*C.) 180 to 660(reduced to 760 mm. Hg)
 3. A method according to claim 1 in which theH.C.G.O. has been dewaxed.
 4. A method according to claim 1 in which theH.C.G.O. has been enriched in aromatic compounds by the use of a solventextraction process.
 5. A method according to claim 1 in which theH.C.G.O. has been topped by distillation.
 6. A method according to claim1 in which the H.C.G.O. has been subjected to an acid treatment.
 7. Amethod according to claim 1 in which the H.C.G.O. forms from 3.5 to 25wt. percent relative to the base oil.
 8. A method according to claim 1in which the coal oil has the following properties: Density at 15* C.1.00 to 1.20 Flash point (open vessel) 120* to 200* C. Refractive Indexat 60* C. 1.63 to 1.67 Pour Point (*C.) -50 to +30 Sulfur (wt.%) 0.3 to0.9 Nitrogen (wt.%) 0.6 to 1.0 C/H atomic ratio 1.35 to 1.65
 9. A methodaccording to claim 8 in which the coal oil has been selected from theanthracene oils known as ''''pale at -5* C.'''' and ''''pale at 0*C.''''
 10. A method according to claim 1 in which the base oil is araffinate derived from a solvent extraction process.
 11. A methodaccording to claim 1 in which the base oil, H.C.G.O. and coal oil aresubjected to a refining process in any combination, the refining processcomprising contact with a natural earth or hydrotreatment.
 12. A stablemineral oil made by a process in accordance with claim
 1. 13. A stablemineral oil comprising a base oil of low aromatic content, from 2 to 50wt. percent of heavy cycle gas oil and 0.2 to 1.0 wt. percent of coaloil, the heavy cycle gas oil having the following properties: Density at15* C. 0.990 to 1.100 Viscosity at 98.9* C. 2 to 8 cst. Aniline Point25* to 80* C. Distillation range 180* to 660* C. (reduced to 760 mm. Hg)and the coal oil having the following properties: Density at 15* C. 1.00to 1.20 Flash Point (open vessel) 120* to 200* C. Refractive Index at60* C. 1.63 to 1.67 Pour Point (*C.) -50 to +30 Sulfur (wt.%) 0.3 to 0.9Nitrogen (wt.%) 0.6 to 1.0 C/H atomic ratio 1.35 to 1.65
 14. A stablemineral oil according to claim 13 in which at least one of the base oil,heavy cycle gas oil and coal oil has been hydrotreated, in anycombination with the other oils.
 15. A stable mineral oil according toclaim 14 in which the heavy cycle gas oil has been dewaxed.
 16. A stablemineral oil according to claim 15 in which the heavy cycle gas oil is adewaxed solvent extract of a topped heavy cycle gas oil fraction.
 17. Astable mineral oil according to claim 16 in which the base oil is amineral oil of relatively low aromatic content and the heavy cycle gasoil is a dewaxed solvent extract of an acid-treated, topped heavy cyclegas oil fraction.
 18. A concentrate for stabilizing mineral oils tooxygen which consists essentially of about 28 to 99.8 wt. percent heavycycle gas oil (H.C.G.O.) and 72 to 0.2 wt. percent coal oil.
 19. Amethod as claimed in claim 1 wherein said composition is more stablethan one made solely from said distillate oil and 2 to 50 wT. percent ofsaid heavy cycle gas oil or one made solely from said distillate oil and0.2 to 1.0 wt. percent of said coal oil.